The irradiation of a finite target volume by means of x-rays from different spatial directions, such as is implemented for instance for the purposes of imaging in diagnostic methods or dose synthesis in therapeutic methods, usually requires as homogenous a gross illumination of the target volume as possible.
Since the x-ray sources usually have a preferred beam direction, along which the maximum dose is located, and the beam direction is usually aligned toward the center of the target volume, the illumination of the boundary areas of the target volume is usually reduced compared with the center of the target volume.
The problem with radiation therapy devices and with imaging devices was previously solved by a beam flattening filter, which flattens the central portions of the radiation lobe and thus homogenizes the profile of the x-ray beam.